Thursday, April 08, 2010

The Eel Mystery

A study on eel study published in the online edition of the Journal of Heredity authored by Joshua Reece a graduate student in biology in Arts & Sciences at Washington University in St. Louis and co-authored by Bowen, Allan Larson, PhD, professor of biology at Washington University and Reece’s advisor, and two biology undergraduate students at Washington University: Kavita Joshi, and Vadim Goz, makes very interesting reading. It is akin to a mystery novel.

Joshua Reece was startled to find seven species eels eating the same thing and, quite literally, living under the same rock. He asks “how cans this happen? Species don’t do that; if they exploit the same niche they don’t diversify, and if they diversify they don’t exploit the same niche.”

Reece and his colleagues collected two species of eels, the undulated moray (Gymnothorax undulatus) and the yellow-edged moray (G. flavimarginatus) from different locations across the Indo-Pacific Ocean, covering two-thirds of Earth’s surface. They were interested in finding out the genetic differences that might indicate interruptions in gene flow among populations of the eels now or in the past. They found both species to be genetically homogeneous across the entire ocean basin.

The mystery now takes a twist. How did these two species and the other 150 species of moray eel in the Indo-Pacific formed separate species?

The mechanism for speciation is geographic isolation. If one group gets separated from the other, by say a mountain range, natural selection and genetic drift gradually remodel the two similar groups into two dissimilar ones. Now we have to see whether there are barriers in the ocean that play the same role in speciation as the mountain ranges do on land. Eastern Pacific Barrier and the Sunda Shelf might be doing this but needs deeper probe.

The scientist looked at selected mitochondrial and nuclear genes and asked whether there were unique alleles of these genes and whether the degree of variance was correlated to geographic separation. They found lots of variation among the eel genes but virtually none of it had any geographic structure. The same alleles are found in South Africa as you do in Panama.

The scientists are keen to crack the mystery. If both species of eel are able to maintain genetic connectivity across the entire ocean basin, how did the species arise in the first place? When and how did they form separate species if their larvae make them nearly impervious to geographic isolation? Many of eel species share habitat, share distributions and share prey items. When that happens as per rule of thumb one species outcompetes the other and the loser fade in to oblivion. The rules don’t seem to apply to the morays and nobody has a clue to this mystery right now.